javascript - Nodejs send to specific user get Cannot read property 'emit' of undefined error -

i want send message specific user connected , logging server sample code, error:

cannot read property 'emit' of undefined 

this below code sample test:

var socket      = require('socket.io'),     express     = require('express'),     app         = express(),     server      = require('http').createserver(app),     io          = socket.listen(server),     port        = process.env.port || 3000,     redis       = require("redis"),     redisclient = redis.createclient();  var io_redis    = require('socket.io-redis');  io.adapter(io_redis({host: 'localhost', port: 6379}));  io.sockets.on('connection', function (socket) {      socket.on('login', function (data) {             console.log(data.username);             login(data.username, data.password, function (success, value) {                 if (success) {                     redisclient.set([data.username, socket.id]);                     socket.emit('login', {result: true, id: value});                 } else {                     socket.emit('login', {result: false});                 }             });         });      socket.on('message', function (username) {                 redisclient.get(username, function (err, socketid) {                     io.sockets.connected[socketid].emit('message', 'hey !!');                 });             }); }); 

why error: search , read many pages of solution far know code seemd correct, don't know whats problem.

error line of code:

io.sockets.connected[socketid].emit('message', 'hey !!'); 

1. not sure why didn't provide line number failed. have multiple emits.
2. who says socket there when redis finishes? must check if exists.

//when set, wait set finish before doing emit('login') //also fixed set, instead of array, put key , value redisclient.set(data.username, socket.id, function (err, done) { if (err) { //now what? } else { socket.emit('login', {result: true, id: value}); } });

//when get, check exists redisclient.get(username, function (err, socketid) { if (io.sockets.connected[socketid]) { io.sockets.connected[socketid].emit('message', 'hey !!'); } });

3. you have

   var socket = require('socket.io'),

and function (socket) {

so defined socket twice. thats not great.